Most synthetic silica is bound with nanosized particles to be manufactured as microsized particles and forms a large specific surface area due to the nanosized particles. An inside of the synthetic silica has a large specific surface area by compression-molding the nanosized particles, and thus the synthetic silica has low thermal conductivity, thereby manufacturing an insulator having good insulation performance.
The so manufactured insulator is used alone or is covered with an outer cover of a glass fiber, and the like for strength reinforcement and used as a vacuum insulator by being sealed with an outer cover of a multilayer film of an aluminum material.
A core of the insulator of the synthetic silica has a large specific surface area due to small pores formed therein and thus the insulator has low thermal conductivity, such that insulation performance of the insulator may be improved.
Generally, a binder needs to be used to have moldability at the time of manufacturing the insulator using the synthetic silica particles. Even though a small amount of binder is used, the synthetic silica has a reduced specific surface area formed therein due to the binder. In particular, particles having many pores formed therein, such as synthetic silica, absorb a considerable amount of liquid phase binder and therefore may hardly be dispersed uniformly.
Due to the phenomenon and since it is difficult to completely dry moisture included in the binder, the thermal conductivity is increased and the insulation performance may be reduced correspondingly.
To solve the above problems, products using an inorganic fibrous mat as an outer cover have been commercialized. However, the synthetic silica itself may be used at 800 to 900° C. or more, but the inorganic fiber may have a limited use temperature according to a kind of inorganic fiber, which is a factor of increasing material costs and increasing prices of an insulator due to additional processing. A general glass fiber has a limited use temperature of about 650° C. and a ceramic fiber may be used at 800 to 900° C. or more, but needs to use a biodegradable material which has no effect on a human body and therefore is expensive.
Further, the insulator has a core enclosed with the outer cover of the multilayer film of an aluminum material and has an inside subjected to vacuum processing, and thus is used as a core of a vacuum insulator having insulating physical property which is thermal conductivity of 0.005 W/mK or less.
Meanwhile, a core of the vacuum insulator relies on long-term durability (service life) which relies on whether the internal vacuum is damaged. A degree of vacuum is damaged by a damage of the outer cover and out gassing which is generated due to internal moisture, organic matters, and the like. The vacuum damage may be prevented by a getter, but may be completely prevented.
In “Thermal Insulation And Method Of Producing thereof” of Korean Patent Laid-Open Publication No. 10-2011-0042019, a method for using alkali-earth metals hydroxide and alkali metal hydroxide so as not to use a binder and curing the alkali-earth metals hydroxide and the alkali metal hydroxide under high humidity and drying them again has been proposed. However, the method has a problem in that a process may be complicated, and moisture may be absorbed into the insulator at the time of the high-humidity curing and thus it may be difficult to completely remove the internal moisture even though the alkali-earth metals hydroxide and the alkali metal hydroxide is dried again.
In “Method Of Manufacturing High Temperature Insulation Flexible Blanket Formed Of Silica Aerogel With Non-woven Glass Fibre Batting And, The Blanket Manufactured By The Method” of Korean Patent Laid-Open Publication No. 10-2010-0083543, a method for stacking an insulator manufactured by producing a non-woven film of a chemical fiber, a carbon fiber, a glass fiber, and the like, applying an organic adhesive on the non-woven film, and adsorbing silica areogel thereon and stitching the insulator with a W-shaped needle has been proposed. However, the method uses a non-solvent type organic adhesive to somewhat prevent the organic adhesive from being absorbed into the silica aerogel but has a problem in that a process may be complicated, manufacturing costs may be increased, and adhesion with the organic adhesive after the manufacturing may be weak to generate dust.